Silver-containing photothermographic imaging materials that are developed with heat and without liquid development have been known in the art for many years. Such materials are used in a recording process wherein
an image is formed by imagewise exposure of the photothermographic material to specific electromagnetic radiation (for example, visible, ultraviolet or infrared radiation) and developed by the use of thermal energy.
These materials, also known as “dry silver” materials, generally comprise a support having coated thereon: (a) photosensitive catalyst (such as silver halide) that upon such exposure provides a latent image in exposed grains that is capable of acting as a catalyst for the subsequent formation of a silver image in a development step, (b) a non-photosensitive source of reducible silver ions, (c) a reducing composition (usually including a developer) for the reducible silver ions, and (d) a hydrophilic or hydrophobic binder. The latent image is then developed by application of thermal energy.
The imaging arts have long recognized that the field of photothermography is distinct from that of photography. Photothermographic materials differ significantly from conventional silver halide photographic materials that require processing with aqueous processing solutions.
For example, in photothermographic imaging materials, a visible image is created by heat as a result of the reaction of a developer incorporated within the material. In contrast, conventional photographic imaging materials require processing in aqueous processing baths at moderate temperatures to provide a visible image.
In photothermographic materials, a small amount of silver halide is used to capture light and a non-photosensitive source of reducible silver ions (for example, a silver carboxylate) is used to generate the visible image using thermal development. Thus, the imaged photosensitive silver halide serves as a catalyst for the physical development process involving the non-photosensitive source of reducible silver ions and the incorporated reducing agent. In contrast, conventional wet-processed, black-and-white photographic materials use only one form of silver (that is, silver halide) that, upon chemical development, is itself converted into the silver image, or that upon physical development requires addition of an external silver source (or other reducible metal ions that form black images upon reduction to the corresponding metal). Thus, photothermographic materials require an amount of silver halide per unit area that is only a fraction of that used in conventional wet-processed photographic materials.
U.S. Pat. No. 6,582,892 (Kong), commonly assigned and incorporated herein by reference, describes a heat-stabilized thermally developable imaging material. As disclosed in U.S. Pat. No. 6,582,892, photothermographic materials can be used, for example, in conventional black-and-white photothermography, in electronically generated black-and-white hardcopy recording. They can be used in microfilm applications, in radiographic imaging (for example, digital medical imaging), and industrial radiography. The absorbance of these photothermographic materials between 350 and 450 nm is desirably low (less than 0.5), to permit their use in the graphic arts area (for example, imagesetting and photo-typesetting), and in proofing. Thermally developable materials have gained widespread use in several industries, particularly in radiography. Thus, photothermographic materials are useful for medical radiography to provide black-and-white images.
Such photothermographic materials can be sensitive to radiation at a wavelength of at least 700 nm, and at a wavelength of from about 750 to about 1400 nm.
Photothermographic materials are processed in a thermal processor that employ heat to develop the material to generated a developed image. While photothermographic materials have been well received in the industry, there continues a need to improve the characteristics of photothermographic materials, such that when processed, a high quality processed image is provided.